Method of forming a power tool

ABSTRACT

An electric motor for a power tool includes a stator and an armature disposed in the stator. The armature includes a lamination stack having slots therein; an armature shaft extending coaxially through the lamination stack; a plurality of magnet wires wound in the slots of the lamination stack; a commutator disposed on the armature shaft to which ends of the magnet wires are electrically coupled; and thermally conductive plastic at least partially encasing the magnet wires, the thermally conductive plastic having a base polymer that is a blend of at least two polymers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/472,829, filed on May 16, 2012, which is a divisional of 12/895,176,filed on Sep. 30, 2010, (now U.S. Pat. No. 8,203,239, issued Jun. 19,2012), which is a divisional of U.S. patent application Ser. No.11/491,457, filed on Jul. 21, 2006 (now U.S. Pat. No. 7,814,641, issuedOct. 19, 2010), which is a divisional of U.S. patent application Ser.No. 10/616,871 filed on Jul. 10, 2003 (now U.S. Pat. No. 7,096,566,issued Aug. 29, 2006), which claims priority under 35 USC 119(e) to U.S.Provisional Application No. 60/395,251, filed on Jul. 12, 2002, and isalso a continuation-in-part of U.S. patent application Ser. No.10/365,065, filed on Feb. 12, 2003 (now U.S. Pat. No. 7,013,552, issuedMar. 21, 2006), which is a divisional of U.S. patent application Ser.No. 09/836,517, filed on Apr. 17, 2001 (now abandoned), which is acontinuation-in-part of U.S. patent application Ser. No. 09/756,959filed Jan. 9, 2001 (now abandoned).

TECHNICAL FIELD

This invention relates to dynamoelectric machines, and more particularlyto a dynamoelectric machine having a coil structure encapsulated with athermally conductive plastic.

BACKGROUND OF THE INVENTION

Dynamoelectric machines are machines that generate electric power or useelectric power. Common types of dynamoelectric machines are alternators,generators, and electric motors.

Electric motors are used in a wide variety of applications involvingpower tools such as drills, saws, sanding and grinding devices, yardtools such as edgers and trimmers, just to name a few such tools. Thesedevices all make use of electric motors having an armature and a field,such as a stator. The armature is typically formed from a laminationstack or core around which a plurality of windings of magnet wires arewound. The lamination stack is formed to have a plurality of polesaround which the magnet wires are wound. In this regard, the laminationstack may be formed with a plurality of slots in which the magnet wiresare wound. Insulators are typically provided between the magnet wiresand the lamination stack. Magnet wires, as that term is commonlyunderstood, are wires of the type conventionally used to wind coils inelectric machines, such as armatures and stators. The magnet wires arecoupled at their ends to a commutator, such as to tangs when thecommutator is a tang type commutator, disposed on an armature shaftextending coaxially through the lamination stack.

The stator is also typically formed from a lamination stack around whicha plurality of windings of magnet wires are wound. The ends of themagnet wires typically have terminals affixed that are then coupled to asource of electrical power. The lamination stack is formed to have aplurality of poles around which the magnet wires are wound. In thisregard, the lamination stack may be formed with a plurality of slots inwhich the magnet wires are wound. Insulators are typically providedbetween the magnet wires and the lamination stack.

In the manufacturing process for the armature described above, once themagnet wires have been secured to the commutator, a “trickle” resin isapplied over the magnet wires and over the ends of the magnet wireswhere they attach to tangs associated with the commutator. The processof applying the trickle resin is a somewhat difficult process to manageto obtain consistent results. It also has a number of drawbacks, not theleast of which is the cost and difficulty of performing it withreliable, consistent results.

Initially, the trickle process requires the use of a relatively largeand expensive oven to carefully preheat the partially assembledarmatures to relatively precise temperatures before the trickle resincan be applied. The temperature of the trickle resin also needs to becarefully controlled to achieve satisfactory flow of the resin throughthe slots in the lamination stack of the armature. It has proven to beextremely difficult to achieve consistent, complete flow of the trickleresin through the slots in the lamination stack. As such, it isdifficult to achieve good flow inbetween the magnet wires with thetrickle resin. A cooling period must then be allowed during which air istypically forced over the armatures to cool them before the nextmanufacturing step is taken. Further complicating the manufacturingprocess is that the trickle resin typically has a short shelf life, andtherefore must be used within a relatively short period of time. Themanufacturing process for making wound stators may involve a similartrickle resin process.

Referring to FIG. 1, there is illustrated a prior art armature 10 madein accordance with a conventional manufacturing process incorporatingthe trickle resin application steps described hereinbefore. The armature10 incorporates a lamination stack 12 having a plurality of longitudinalslots 14 disposed circumferentially therearound. Wound within the slots14 is a large plurality of magnet wires 16 forming coils. An armatureshaft 18 extends coaxially through the lamination stack 12 and includesa commutator 20. An independently formed plastic fan 22 is secured,typically by adhesives, to the lamination stack 12. The fan 22 typicallyincludes a plurality of legs 24 which project into the slots 14, thustaking up space which would more preferably be occupied by the magnetwires 16. Trickle resin 26 is applied over the magnet wires 16, in theslots 14, and also at the tangs 25 where the ends 16 a of the magnetwires 16 attach to the commutator 20.

Abrasive particles are drawn in and over the armature by the armature'sfan, particularly when the armature is used in tools such as grindersand sanders. As shown particularly in FIG. 2, the air flow, shown byarrows 30, impinges magnet wires 16 of end coils 17 (the portion of thecoils of magnet wires that extend around the ends of the laminationstack 12 between the slots 14 in the lamination stack 12). The air flow30 contains abrasive particles and the impingement of these abrasiveparticles on magnet wires 16 can wear away the insulation of magnetwires 16.

With present day manufacturing techniques, an additional or secondaryoperation is often required to protect the armature (and specificallythe magnet wires) from the abrasive particles. Such secondary operationsinclude a coating of higher viscosity trickle resin, an epoxy coating,or wrapping the wires, such as with cotton, string or the like. Thisserves to further increase the manufacturing cost and complexity of thearmature.

Still another drawback with the trickle process is the relatively highnumber of armatures which are often rejected because of problemsencountered during the process of applying the trickle resin to anotherwise properly constructed armature. Such problems can includecontamination of the commutator of the armature by the trickle resinduring the application process, as well as uneven flow of the trickleresin if the pump supplying the resin becomes momentarily clogged.Accordingly, the difficulty in controlling the trickle resin applicationprocess produces a relatively large scrap rate which further adds to themanufacturing cost of electric motors.

Slot insulators and end spiders of armatures have been formed by insertmolding the armature shaft and lamination stack in plastic. FIG. 3 showssuch a prior art armature 40 having a lamination stack 42 on a shaft 44.Lamination stack 42 has a plurality of slots 46. The plastic is moldedunderneath the lamination stack 42 and around shaft 44 to insulate theshaft 44 from the lamination stack 42. The plastic is also molded toform end spiders 48 and molded in slots 46 to form slot liners 50. Slotliners 50 insulate the windings 52 from lamination stack 42 after thewindings 52 have been wound in the slots 46 to form coils 54.

The plastic used in molding the prior art armature 40 has been plasticthat is not thermally conductive, such as nylon or PPS. This can resultin problems in dissipating the heat generated in the coils 54 during theoperation of the motor in which armature 40 is used.

Most armatures or rotors used in dynamoelectric machines, such as motorsand generators, are dynamically balanced to reduce the vibration forcetransmitted to the motor housing by way of the bearings. Dynamicbalancing requires that material be added to or removed from the ends ofthe armature. The most beneficial places to do this are on planes nearto the bearing planes at the largest possible radius. However, forpractical reasons, universal motor armatures and permanent magnet motorarmatures are usually balanced by selectively removing material from thesurface of the iron core (also called the lamination stack).

This balancing process has a number of disadvantages. First, the planesin which the material are removed are located within the length of thelamination stack and thus are relatively distant from the bearing planeswhere the imbalance forces are transmitted to the rest of the product.Second, removal of material from the motor's active iron core(lamination stack) has a negative effect on performance, particularly,torque ripple. Third, balancing by removing material from the surface ofthe lamination stack requires that the tooth tops of the laminationstack be thicker than needed for spreading magnetic flux. The thickertooth tops rob winding space from the slots in the lamination stack inwhich magnet wires are wound. Fourth, the surface of the laminationstack is not homogenous. It consists of iron at the tooth tops and airor resin in the winding slot area. This non-homogeneity presents a moredifficult computation to the dynamic balancing machine that must decidehow much material to remove and where to remove it from. Consequently,the dynamic balance machines often must make repetitive correctivepasses during which even more iron is removed from the lamination stack,further reducing performance.

Coil stays have typically been used to hold the magnet wires, such asmagnet wires 16, in the slots, such as slots 14, in the laminationstack, such as lamination stack 12. FIG. 4 shows one of slots 14 oflamination stack 12 of prior art armature 10 (FIG. 1) disposed betweenopposed poles 13 of lamination stack 12 and magnet wires 16 wound inslot 14. A slot liner 15, typically made of a paper insulation, isdisposed in slot 14 between the magnet wires 16 and walls of laminationstack 12. Magnet wires 16 are retained in slot 14 by a coil stay 19,which is illustratively made of vulcanized fibers that are bothelectrically and thermally insulative. Such prior art coil stays havecertain undesirable characteristics. First, they occupy space that couldotherwise be filled with magnet wires 16. Second, the poor thermalconductivity of the coil stay material limits the amount of heat thatcan be transferred to the surface of lamination stack 12.

As is known, the power of a motor having magnet wires wound in slots ofa lamination stack is a function of the current flowing through themagnet wires and the number of turns of magnet wires. A motor having agiven output, i.e., 1/10 horsepower, ⅛ horsepower, ¼ horsepower,requires that a certain number of turns of magnet wires that can carry agiven current be used. The ability of the magnet wires to carry thegiven current is a function of the size (diameter) of magnet wires. Thesize of the magnet wires that must be used to wind the given number ofturns of the magnet wires in turn dictates the size of the slots inwhich they are wound. That is, the slots must be large enough to holdthe required number of turns of magnet wires.

If a larger size magnet wire can be used to wind the magnet wires,higher power can be achieved due to the decreased resistance of thelarger size magnet wire compared with the smaller size magnet wire.However, using a larger size magnet wire to wind the magnet wires wouldtypically require larger slots to accommodate the required number ofturns of the larger size magnet wire, which in turn would require alarger lamination stack. Thus the armature would be larger.

Mains driven power tools, tools driven from power mains such as 120 VAC,are often double-insulated to protect the user from electric shock.Double-insulation requires two separate levels of electrical insulation:functional insulation and protective insulation. Functional insulationelectrically insulates conductors from one another and fromnon-touchable dead-metal parts of the armature. An example of anon-touchable dead metal part is the lamination stack of the armature,such as lamination stack 12 (FIG. 1). The functional insulation systemincludes the core insulation, magnet wire film, and the resin matrixthat bonds the whole together. Core insulation could also consist ofepoxy coatings applied by a powder coating process.

The protective insulation consists of an electrically insulative tube orsleeve disposed between the touchable dead-metal shaft, such as shaft 18(FIG. 1), and the rest of the armature structure. The shaft isconsidered touchable since it is in conductive contact with exposedconductive parts of the tool, such as a metal gearbox and/or metalspindle or chuck. In order to provide protection at the end of thetool's functional life due to abusive loads and burnout, the protectiveinsulation barrier must have electrical, thermal, and structuralproperties that are superior to those of the functional insulationsystem. Therefore, the insulating tube or sleeve is usually constructedof high-temperature, glass reinforced thermosetting resin. Othermaterials such as ceramic, mica, and composites of these material couldalso be used to make the insulating tube or sleeve.

SUMMARY OF THE INVENTION

In an aspect of the invention, an armature for an electric motor has anarmature shaft having a lamination stack thereon. The armature shaft andlamination stack are insert molded in thermally conductive plastic. Inan aspect of the invention, the plastic increases stiffness and thusincreases the critical speed of the armature. In an aspect of theinvention, the mass of plastic, its distribution, or both are varied toadjust the spinning inertia of the armature. In another aspect of theinvention, the geometry of the plastic, it mechanical properties, orboth are varied to adjust the resonant frequency (critical speed) of thearmature.

In another aspect of the invention, bondable wire (which is wire thathas a layer of heat activated adhesive thereon) is used to wind thecoils of a coil structure for a dynamoelectric machine, such as anarmature for an electric motor or a stator for an electric motor.Plastic, preferably thermally conductive plastic, is molded around thebondable wire. The heat of the plastic as it is being molded activatesthe heat activated adhesive on the bondable wire, bonding the wirestogether.

In another aspect of the invention, a coil structure for adynamoelectric machine has wires wound in slots in a lamination stackforming coils. Thermally conductive plastic is molded around the wiresat a pressure to at least partially deform the wires into polygonalshapes. The polygonal shapes increase the contact surface area of thewires and enhance heat transfer from the wires.

In another aspect of the invention, the pressure at which the thermallyconductive plastic is molded around the wires is set at a pressure thatcompacts the wires in the slots in the lamination stack that allows forincreased slot fill.

In an aspect of the invention, increased power is achieved by using alarger size magnet wire. The pressure of the plastic being molded is setto compact the magnet wires so that the same number of turns of magnetwires wound with the larger size magnet wire can be used. The largersize magnet wire has a lower resistance per given length compared withthe smaller magnet wires heretofore used for a given size of motor whichresults in increased power when the same number of turns of magnet wireswound with the larger size magnet wire are used. In a variation of thisaspect of the invention, iso-static pressure is used to compact themagnet wires in the slots.

In another aspect of the invention, the plastic is molded aroundarmature lead wires, the portion of the magnet wires leading to thecommutator, and provides support for the armature lead wires.

In another aspect of the invention, thermally conductive plastic ismolded around at least a portion of the magnet wires of an armature toat least partially encase them. In an aspect of the invention, thethermally conductive plastic has thermally conductive additives such asaluminum oxide, boron nitride, or aluminum nitride. In an aspect of theinvention, the thermally conductive plastic has phase change additivestherein. In an aspect of the invention, the plastic can have a basepolymer that is Nylon, PPS, PPA, LCP, or blends.

In another aspect of the invention, the plastic can be a thermoset andin addition to injection molding, transfer molding or compressionmolding used to mold the plastic around the armature.

In another aspect of the invention, a coil structure for adynamoelectric machine has a lamination stack with a plurality of slotstherein. The slots are lined with slot liners formed of thermallyconductive plastic. Wires are wound in the slots to form coils. The slotliners enhance heat transfer out of the wires and also electricallyinsulate the wires from the lamination stack. In an aspect of theinvention, thermally conductive plastic is molded to form the slotliners. In an aspect of the invention, the coil structure is an armaturefor an electric motor and the thermally conductive plastic is alsomolded to form end spiders and to be disposed between the armature shaftand lamination stack, electrically insulating the lamination stack fromthe armature shaft.

In another aspect of the invention, an armature for an electric motorhas a lamination stack on a shaft with a tang type commutator mounted onone end of the shaft. The lamination stack has slots in which magnetwires are wound forming coils. Ends of the magnet wires are attached totangs of the commutator. The commutator has a commutator ring dividedinto a plurality of segments with slots between the segments. Thecommutator is notched around an axial inner end with the notches locatedwhere axial inner ends of the slots will be once the slots are cut. Thenotches are filled with plastic when the commutator is made by molding acore of plastic, such as phenolic, in the commutator ring before thecommutator ring is mounted on the armature shaft. The slots are then cutin the commutator ring to divide it into segments. The slots are cutaxially through the commutator ring and run from an axial distal end ofthe commutator ring part way into the notches at the axial inner end ofthe commutator ring. The magnet wires, commutator and armature shaft areat least partially encapsulated in plastic, such as by insert molding.The mold used to mold the plastic includes projections that extendbetween the tangs of the commutator and against the notches filled withplastic. The notches filled with plastic and the projections of the moldprevent plastic flash from getting into the slots of the commutator ringwhen plastic is molded to at least partially encapsulate the magnetwires, armature shaft, and commutator.

In another aspect of the invention, an armature for an electric motorhas a lamination stack on a shaft with a stuffer type commutator mountedon one end of the shaft. The stuffer commutator has a commutator ringdivided into a plurality of segments by slots between the segments.Insulative inserts extend part way into each slot from an axial innerend of the commutator ring. Axial inner ends of each segment have slotsinto which ends of magnet wires are pressed. The lamination stack hasslots in which the magnet wires are wound forming coils. The magnetwires, commutator and armature shaft are at least partially encapsulatedin plastic, such as by insert molding. The mold used to mold the plastichas a portion that seals around the inner end of the commutator ringabove the inserts to prevent plastic flash from getting into the slotsbetween the segments of the commutator ring when the magnet wires,armature shaft and commutator are at least partially encapsulated withplastic.

In another aspect of the invention, an armature having a laminationstack with slots therein is at least partially encapsulated by moldingthermally conductive plastic around at least parts of it, including inthe slots in the lamination stack and around magnet wires wound in theslots. The plastic is molded in the slots so that the slots are coredout leaving recesses in the slots between teeth of the lamination stack.The recesses reduce the amount of plastic molded, enhance heat transfer,and provide slots for receiving projections of tools used in processingthe armature to properly locate and orient the armature.

In another aspect of the invention, a coil structure for adynamoelectric machine has a lamination stack with a plurality of slotstherein. Magnet wires are wound in the slots to form coils. Thermallyconductive plastic is molded around the magnet wires to at leastpartially encapsulate them. Features, such as fins, texturing, or bothare formed in the surface of the thermally conductive plastic to enhanceheat transfer. In an aspect of the invention, the features aremetallized. In an aspect of the invention, the features are pre-formedand insert molded when plastic is molded around the magnet wires. In anaspect of the invention, the features include a metallic finned cap thatfits over the end coils of the magnet wires.

In an aspect of the invention, elements requiring physical robustness,such as the fan, are pre-formed of higher strength material and insertmolded when plastic is molded around the armature to encapsulate it inwhole or in part.

In another aspect of the invention, the armature is completelyencapsulated with plastic and excess plastic machined off.

In another aspect of the invention, the armature is a double insulatedarmature that is encapsulated, in whole or in part, with plastic. In anaspect of the invention, the double insulated armature has an insulativesleeve that is disposed between a shaft of the armature and a laminationstack and between the shaft and a commutator. In an aspect of theinvention, the insulative sleeve is disposed between the shaft of thearmature and the lamination stack and extends up to the commutator witha seal disposed between the commutator and the insulative sleeve toprevent any plastic from getting into any gap between the insulativesleeve and the commutator when plastic is molded around the armature.

In another aspect of the invention, the armature is a double insulatedarmature having a commutator and lamination stack mounted directly on aninternal shaft. The internal shaft is coupled to an external pinion andbearing journal by means of an insulated barrier.

In another aspect of the invention, the plastic molded around thelamination stack, portions of the commutator and the armature shafthelps holds the commutator and lamination stack on the armature shaftand provides for improved torque twist. In a variation of this aspect ofthe invention, the armature shaft is provided with features, such as oneor more flats, that interlock with the plastic molded around them tofurther improve torque twist.

In an aspect of the invention, a three plate mold is used to mold theplastic around the armature. In a variation, a two-plate mold is usedthat has overflow tab cavities into which plastic flows before flashingover the commutator of the armature around which plastic is beingmolded.

In an aspect of the invention, when thermally conductive plastic ismolded to an encapsulated armature, features are molded to improve theprocess of balancing the armature during dynamic balancing of thearmature. In a variation, plastic at least partially encases the magnetwires with at least one balancing feature formed from the plastic, suchas a layer of the plastic from which plastic can be removed to balancethe armature. Another variation includes at least one balancing ringmolded adjacent an axial side of the lamination stack from which plasticcan be removed to balance the armature. In another variation, the one ormore balancing rings include one or more pockets therein for receiving aweight to balance the armature.

BRIEF DESCRIPTION OF THE DRAWINGS

The various advantages of the present invention will become apparent toone skilled in the art by reading the following specification andsubjoined claims and by referencing the following drawings in which:

FIG. 1 is a side elevation view of a prior art armature whichincorporates the conventional trickle resin coating and separatelymanufactured fan secured by adhesives to the armature;

FIG. 2 is a schematic view of air flow around end coils of a prior artarmature;

FIG. 3 is a perspective view of a prior art armature with plastic moldedin slots in a lamination stack to form slot liners, at the ends of thelamination stack to form end spiders and around a shaft of the armature;

FIG. 4 is a side view of a section of a slot in a lamination stack of aprior art armature with magnet wires held therein by a coil stay;

FIG. 5 is a side elevation view of an armature in accordance with anaspect of the invention;

FIG. 6 is a side elevation view of an armature in accordance with anaspect of the invention;

FIG. 7 is an end view of the armature of FIG. 6;

FIG. 8 is an end view of a variation of the invention shown in FIGS. 6and 7;

FIG. 9 is a coil stay in accordance with an aspect of the invention;

FIG. 10 is a view of a section of a slot in a lamination stack withbondable magnet wires therein with the heat activated adhesive of thebondable magnet wires having been activated by the heat of plastic as itis molded in accordance with an aspect of the invention;

FIG. 11 is a view of a section of a slot in a lamination stack withmagnet wires therein deformed by pressure of plastic molded around themin accordance with an aspect of the invention;

FIG. 12 is a view of a section of a slot in a prior art lamination stackwith magnet wires therein;

FIG. 13 is a view of a section of a slot in a lamination stack withlarger size magnet wires therein in accordance with an aspect of theinvention;

FIG. 14 is a view of a section of a slot in a lamination stack in whichmagnet wires are compressed by iso-static pressure;

FIG. 15 is a view of a section of a stator for an electric motorencapsulated with a thermally conductive plastic in accordance with anaspect of the invention;

FIG. 16 is an end view of a section of a stator with a thermallyconductive plastic molded in slots in a lamination stack to form slotliners in accordance with an aspect of the invention;

FIG. 17 is a perspective view of an armature with a tang type commutatormade so that plastic flash is prevented from getting in slots betweensegments of the commutator in accordance with an aspect of theinvention;

FIG. 18 is a perspective view of a tang type commutator;

FIG. 19 is a view of a mold, shown representatively, used in making thearmature of FIG. 8;

FIG. 20 is a perspective view of an armature with a stuffer typecommutator made so that plastic flash is prevented from getting in slotsbetween segments of the commutator in accordance with an aspect of theinvention;

FIG. 21 is a section view of a partial section of the armature of FIG.11 taken along the line 21-21 of FIG. 20;

FIG. 22 is a perspective view of an armature encapsulated with athermally conductive plastic with features for enhancing heat transferin accordance with an aspect of the invention;

FIG. 23 is a perspective view of another armature encapsulated with athermally conductive plastic with features for enhancing heat transferin accordance with an aspect of the invention;

FIG. 24 is a perspective view of an armature encapsulated with athermally conductive plastic with a necked down region adjacent thecommutator in accordance with an aspect of the invention;

FIG. 25 is a perspective view of an armature having features for heattransfer in accordance with an aspect of the invention;

FIG. 26 is a side view of features of the armature of FIG. 25 formed inaccordance with an aspect of the invention;

FIG. 27 is a side view of features of the armature of FIG. 25 formed inaccordance with an aspect of the invention;

FIG. 28 is a side section view, broken away, of an armature shaft havingfeatures that interlock with plastic molded around them in accordancewith an aspect of the invention to improve twist torque;

FIG. 29 is a perspective view of a double insulated armature inaccordance with an aspect of the invention;

FIG. 30 is a perspective view of another double insulated armature inaccordance with an aspect of the invention;

FIG. 31 is a perspective view of another double insulated armature inaccordance with an aspect of the invention;

FIG. 32 is a side section view of a three plate mold used to encapsulatean armature in accordance with the invention;

FIG. 33 is a top view of the three plate old of FIG. 32;

FIG. 34 is a perspective view of a portion of an armature molded in thethree plate mold of FIG. 32 opposite an end of the armature on which acommutator is affixed;

FIG. 35 is a perspective view of a portion of an armature molded in thethree plate mold of FIG. 32 adjacent a commutator;

FIG. 36 is a portion of a section view of the three plate mold of FIG.32 and a portion of a lamination stack being encapsulated; and

FIG. 37 is a representative view of a two-plate mold having overflow tabcavities in accordance with an aspect of the invention.

DETAILED DESCRIPTION

Referring now to FIG. 5, a motor 100 in accordance with a preferredembodiment of the present invention is disclosed. The motor 100 includesan armature 102 and a stator 104, the stator being illustrated in highlysimplified fashion. The armature 102 incorporates a lamination stack 106having a plurality of longitudinal slots 108 arranged circumferentiallytherearound. A plurality of magnet wires 110 are wound in the slots 108to form a plurality of coil windings having end coils 117. An armatureshaft 112 extends coaxially through the lamination stack 106 and hasdisposed on one end thereof a commutator 114. A thermally conductiveplastic 116 is injection molded over the armature 102 so that theplastic flows into and through each of the slots 108. The thermallyconductive plastic 116 is applied by placing the armature 102 in asuitable injection molding tool and then injecting the thermallyconductive plastic 116 under a suitably high pressure into the moldingtool. The thermally conductive plastic 116 preferably at least partiallyencases the magnet wires 110, and more preferably completely encases themagnet wires to form an excellent means for transferring heat therefrom.The plastic 116 also encases the ends 118 of armature lead wires 119 ofthe magnet wires 110 which are secured to tangs 120 operably associatedwith the commutator 114.

A fan 122 is also integrally formed during the molding of the thermallyconductive plastic 116 at one end of the lamination stack 106. Formingthe fan 122 as an integral portion of the thermally conductive plastic116 serves to completely eliminate the manufacturing steps in which atrickle resin is applied to the lamination stack 106 and then aseparately formed fan is adhered to the lamination stack 106.

The molding of the thermally conductive plastic 116 to substantially orcompletely encase the magnet wires 110 serves to efficiently conductheat away from the magnet wires. Thus, the thermally conductive plastic116 even more efficiently serves to secure the magnet wires 110 to thelamination stack 106 to prevent movement of the wires, as well as tosecure the magnet wires to the tangs 120 and to improve the conductionof heat from the wires.

The molding of the fan 122 as an integral portion of the thermallyconductive plastic coating 116 also provides a significant manufacturingbenefit by removing the cost associated with separately forming such afan component and then securing the component via an adhesive to thelamination stack 106. This allows the fan 122 to be constructed evenmore compactly against the lamination stack 106 which allows a motor tobe constructed which requires less space than previously developedmotors employing independently formed fans.

Another advantage of having the fan 122 molded from the thermallyconductive plastic is that the fan will be even more resistant to hightemperatures which might be encountered during use which stresses themotor 100. With previously developed motors, the fan mounted to thearmature thereof is often the first component to fail because of hightemperatures encountered during periods of high stress of the motor. Thearmature 102 of the present invention, with its integrally molded fan122, is significantly more resistant to failure due to hightemperatures.

The injection molding of a thermally conductive plastic may also moreefficiently fill the spaces and voids inbetween the magnet wires 110extending through the lamination stack slots 108, thus promoting evenmore efficient cooling of the armature 102 during use.

In an aspect of the invention, plastic 116 is molded to completelyencapsulate all the elements of armature 102, including lamination stack106 and commutator 114. Thereafter, excess plastic 116 is removed fromarmature 102, such as by machining, to expose those portions of armature102 that need to be exposed, such as the surface of commutator 114 andthe surface of lamination stack 106.

Encapsulation also provides enhanced mechanical retention of magnetwires 110 and can be used in lieu of the adhesive typically used tosecure the armature lead wires 119. Particularly in high vibrationapplications, the armature lead wires must be supported, that is,affixed in place. Otherwise, rotation of the armature and vibration ofthe device in which the motor having the armature is used, such as apower tool, can cause the armature lead wires to vibrate and eventuallyfatigue and break. Typically, during the trickle resin process describedabove, a high viscosity adhesive is applied around the armature leadwires up to where they attach to the commutator. This adhesive providesthe required support for the armature lead wires.

Plastic 116 is illustratively molded around armature lead wires 119 whenplastic 116 is molded around magnet wires 110. Plastic 116 provides thenecessary support for the armature lead wires 119 to prevent them fromvibrating when the armature 102 rotates and the device, such as a powertool having a motor using armature 102 vibrates. The armature lead wires119 can thus be supported by the encapsulation of plastic 116 at littleor no additional cost. Moreover, the enhanced mechanical retentionprovided by encapsulation allows larger gauge magnet wires 110 to beemployed on a given size armature, thus increasing the amp rating whichcan be attained with a motor of given dimensions over a comparably sizedmotor employing trickle resin sealing of the magnet wires. The largergauge magnet wires 110 provide better heat transfer and lower heatgeneration, as well as lower resistance as discussed below.

The thermally conductive plastic 116 is a illustratively base polymer,such as nylon (nylon 4,6, for example), PPS, PPA, liquid crystal polymer(LCP), or a blend of these, with an appropriate fill percentage of athermally conductive material such as ceramic (abrasive or lubricious)and, illustratively, an appropriate amount of glass fill for strength.Aluminum oxide is a common type of abrasive ceramic used in thermallyconductive plastic and boron nitride is a common type of lubriciousceramic. It should be understood that other thermally conductivematerials, metallic or non-metallic, can be used as the fill material,such as aluminum nitride, aluminum or copper. By using a blend for thebase polymer, some of advantages of using a more expensive polymer, suchas LCP, can be realized without incurring the cost of using 100% of themore expensive polymer as the base polymer. For example, blending LCPwith PPS at a ratio of about 10% LCP to 90% PPS increases moldabilityand strength compared to pure PPS. Similarly, a small amount of nyloncould be used instead of LCP.

Thermally conductive plastic 116 can illustratively be Konduit®thermoplastic commercially available from LNP Engineering Plastics ofExton, Pa. (presently a General Electric company). In this regard, thethermally conductive plastic 116 can illustratively be Konduit®PDX-TF-212-11 modified to have about ten percent more ceramic fill.

In an aspect of the invention, a “phase change additive” is added to thematerial used to encapsulate the armature. As used herein, a “phasechange additive” is a material that changes phases, such as from solidto liquid or liquid to gas, at a temperature that is below thetemperature at which the material used to encapsulate the armature meltsbut above ambient temperatures. Preferably, the phase change material isone that changes phases from solid to liquid. The phase change additivewould increase the capability of the encapsulation material, such asthermally conductive plastic 116, to handle short term heat spikes thatit might not otherwise be able to dissipate quickly enough. When heatspike occurs, the phase change additive changes phase absorbing heat.The phase change additive may illustratively be compounded in smallspheres or particles that are added to the plastic used to encapsulatethe armature. The capacity of the plastic encapsulating the armature towithstand short heat spikes can then be adjusted by adjusting the amountof phase change additive that is added to it. By using the phase changeadditive, plastic having lower thermal conductivity, that may be lessexpensive, can then be used to encapsulate the armature. Use of thephase change additive could also increase the capacity of plastic 116 towithstand the additional heat generated in spikes in more demandingapplications. Phase change additives can include parafins, waxes,hydrated salts and possibly crystalline plastics such as acetal ornylon. An example of a hydrated salt phase change additive is the TH89°C. available from TEAP Energy of Wangar, Perth Western Australia.

While plastic 116 is illustratively a thermally conductivethermoplastic, other types of materials can be used to encapsulatearmature 102, including thermoset materials, as long as the material iselectrically non-conductive and has sufficient dielectric strengththroughout the operating temperature of armature 102. In this regard,plastic 116 should illustratively have a dielectric strength of at least250 volts/mil. up to a temperature of 300° C. when armature 102 is usedin a power tool. Further, in those aspects of the invention wherethermal conductivity of the encapsulating material is not needed, thenit need not be thermally conductive. In this regard, while theencapsulation process has been described in the context of injectionmolding, it should be understood that other processes could be used,such as transfer molding or compression molding. The process used would,of course, need to be suitable for the material being used toencapsulate the armature. For example, transfer molding and compressionmolding are typically used to mold thermoset materials and injectionmolding used to mold both thermoplastic and thermoset materials.

With the armature 102, the thermally conductive plastic 116 may comprisea high temperature nylon or thermoset material which is further mixedwith a suitable non-ferromagnetic material such as ceramic, aluminum orcopper, to provide essentially the same density as that of the magnetwires 110. Thus, when each of the lamination stack slots 108 arecompletely filled with the plastic 116 and the magnet wires 110, theweight of the material filling each slot 108 is essentially the same.Since the weight of the material filling each slot 108 is essentiallythe same, the need to balance the armature on a balancing machine, afterthe molding step, is eliminated. Eliminating the balancing steprepresents a substantial cost savings because no longer is the use of abalancing machine required, as well as the manual labor of setting eachof the armatures up on the balancing machine. Instead, once thearmatures have cooled after the injection molding process, the armaturescan proceed to the commutator turning operation and then directly to theassembly stage where they are assembled with other components to formmotors. LNP Engineering Plastics, Inc. is a source of specificallyformulated plastics.

Turning to FIGS. 6 and 7, another aspect of the invention is described.Elements in common with FIG. 5 will be identified with the samereference numerals. When plastic 116 is molded to encapsulated armature102, features are molded to improve the process of balancing armature102. These features illustratively include one or more of extrasacrificial material molded at the periphery of end coils 117 (FIG. 2)formed by the windings of magnet wires 110 or molded pockets that mayreceive balance weights. Utilizing such features in the balancing ofarmature 102 eliminates the machining of non-homogenous material,eliminates the removal of active iron, permits the thickness of theteeth tops of the teeth of lamination stack 106 to be smaller, andlocates the balance planes nearer to the bearing planes allowing truerbalancing with less material removed or added.

Referring specifically to FIG. 6, armature 102 includes one or morebalancing rings 124 molded of plastic 116 when plastic 116 is molded toencapsulate armature 102. Illustratively, a balancing ring is moldedadjacent each axial side of lamination stack 106 over end coils 117.With specific reference to FIG. 7, during balancing of armature 102,material is removed from one or more of the balancing rings 124 at oneor more points 126. Balancing rings 124 are located closer to thebearing planes (not shown) of the motor (not shown) using armature 102and are inert, that is, do not include active iron. Consequently,removing material from balancing rings 124 does not affect the magneticcharacteristics of lamination stack 106 and thus does not adverselyaffect the performance of the motor in the way that removing iron fromlamination stack 106 does.

In a variation, balancing rings 124 have pockets or cavities 128 formedtherein. During balancing of armature 102, weights 130 are inserted andfixed in one or more pockets 128 (FIG. 8) (only one of which isidentified by reference numeral 128) of one or more of balancing rings124 to balance armature 102. Weights 130 are also located nearer thebearing planes and are also inert. In this variation, balancing rings124 can be made lighter.

In another aspect of the invention, the mass of plastic 116, thedistribution of the molded plastic 116, or both, can be varied to adjustthe spinning inertia of armature 102. The mass of plastic 116 can bevaried by varying the amount of plastic 116 used, varying its density,or both. The density of plastic 116 can be varied by, for example, theamount of non-ferromagnetic material mixed with plastic 116. Thedistribution of the molded plastic 116 controls the spinning inertia ofarmature 102 by placing more or less plastic 116 around the axis ofarmature shaft 112, such as closer to or further away from the axis ofarmature shaft 112.

Armatures, as is known, have a natural frequency at which they resonate,commonly referred to as the resonant frequency. This frequency is afunction of the geometry and stiffness of the armature. In anotheraspect of the invention, the natural or resonant frequency of armature102 can be adjusted by varying the geometry, physical and/or mechanical(physical) properties of plastic 116. Varying the geometry, physicaland/or mechanical (such as its tensile or flexural modulus) propertiesof plastic 116 varies the stiffness of armature 102. For example,increasing the physical (such as density, hardness, or both) of plastic116 provides vibration damping for armature 102. Also, increasing thestiffness of armature 102 increases its critical speed, that is, therotational speed at which armature 102 resonates. The critical speed ofthe armature is often the limiting factor of how fast a motor can spinin that its speed must be kept below the critical speed. By increasingthe critical speed, the maximum speed at which the motor can be run isincreased, which increases the output power that the motor can provide.For example, applicants have found that using an encapsulated armaturein a small angle grinder (a DeWalt DW802 SAG), the critical speed of thearmature was increased about 11.5%, that is, from 39,300 RPM to 43,800RPM.

Plastic 116 also provides structural reinforcement around armature shaft112 to reduce and/or control vibration and flexing of armature shaft112. The geometry and mechanical properties of plastic 116 can beadjusted to obtain the desired vibration and/or flex reduction/controlof armature shaft 112.

Bondable wire is typically used to adhere wires, such as magnet wires ina field, together without the addition of glue or varnish in a secondaryoperation, such as the above described trickle resin operation. Bondablewire has a layer of material thereon that becomes sufficiently viscouswhen hot that it adheres together adjacent wires in the bundle of wiresforming the coil and then hardens to bond the wires together. This formsa coil that is mechanically solid and also has improved thermalproperties due to the reduction of air pockets between wires. One typeof bondable wire has a layer of heat activated adhesive thereon. A typeof this bondable wire having a layer of heat activated adhesive thereonis available under the trade name BONDEZE from Phelps Dodge of FortWayne, Ind.

With reference to the embodiment described in FIG. 5, when the thermallyconductive plastic 116 is molded around magnet wires 110, thermallyconductive plastic 116 may not fill all the interstitial voids betweenthe magnet wires 110. In another aspect of the invention, magnet wires110 can be bondable wires that are then encapsulated in a hotencapsulation material. In an embodiment, the bondable wire is BONDEZEwire. The heat of the hot encapsulation material, such as injectionmolded thermally conductive plastic 116, activates the layer of heatactivated adhesive on magnet wires 110, bonding magnet wires 110together.

FIG. 10 shows slot 108 having magnet wires 110 encapsulated in thermallyconductive plastic 116 where the heat of the thermally conductiveplastic as it was molded around magnet wires 110 activated heatactivated adhesive 111 bonded magnet wires 110 together. This forms amechanically solid coil inside thermally conductive plastic 116. Thisreduces or prevents movement of the coil and improves thermal transfer,as described above. This aspect of the invention further contributes tothe elimination of the need for the trickle resin process of bonding themagnet wires together. Further, the heat generated during the moldingprocess activates the heat activated adhesive obviating the need toseparately, activate the heat activated adhesive 111, such as by bakingin an oven or passing a current through magnet wires 110 to heat them toactivate the heat activated adhesive. For this aspect of the invention,the temperature of the encapsulation material being used just needs toexceed the temperature required to activate the heat activated adhesiveon the magnet wire 110.

Turning to FIG. 11, another aspect of this invention is described. FIG.11 shows magnet wires 110 in one of lamination slots 108 encapsulated bythermally conductive plastic 116. By setting the pressure at which theplastic 116 is molded around magnet wires 110 at a sufficiently highlevel, magnet wires 110 can be at least partially deformed intopolygonal shapes from their original round shape. This increases thesurface area contact between magnet wires 110 and thus improves thermalconductivity from the bottom magnet wires 110 through the other magnetwires 110 into thermally conductive plastic 116. It is thought that theforegoing is advantageous when the diameter of magnet wires 110 or thefill pattern of magnet wires 110 (such as how close they are compactedtogether) prevents each magnet wire 110 from being completely surroundedby thermally conductive plastic 116.

In another aspect of this invention, the pressure at which the plastic116 is molded around magnet wires 110 is set at a sufficiently highlevel to compact the wires together, providing for an increased fillrate in lamination slots 108. That is, a higher percentage of the volumeof lamination slots 108 is filled with magnet wires. In this regard,magnet wires 110 may be initially wound in lamination slots 108 so thatthey extend close to or even beyond an outer surface of lamination stack106. The pressure of the plastic 116 as it is molded then compacts themagnet wires 110 together and forces the compacted magnet wires 110 intoslots 108.

In an aspect of the invention, coil stays 19 (FIG. 4A) are made ofthermally conductive plastic that is melted or wetted during molding ofplastic 116.

In an aspect of the invention, plastic 116 replaces coil stays 19 ofprior art armature 10, and holds magnet wires 110 in place when ithardens.

In an aspect of the invention, coil stays 19′ (FIG. 4B) have holes 142therein. During molding of plastic 116, plastic 116 flows through andbypasses coil stays 19′. Plastic 116 is illustratively a thermallyconductive plastic, as described, and molding it through holes 142 incoil stays 19′ allows more heat to flow toward the surface of thelamination stack, such as lamination stack 106 (FIG. 5).

With reference to FIGS. 12 and 13, a larger size magnet wire is used towind magnet wires 110 (FIG. 13) than to wind magnet wires 16 (FIG. 12).Slots 14 in FIG. 12 and slots 108 in FIG. 13 are the same size. In theembodiment of FIG. 13, plastic 116 is molded at pressure around magnetwires 110 compacting them together in slots 108 allowing slots 108 toaccommodate the magnet wires 110 wound with the larger size magnet wire.Magnet wires 110 can thus be a larger size magnet wire compared tomagnet wires 16 of FIG. 12. Thus, magnet wires 110 wound in slots 108 ofa given size, which dictates in large part the size of the laminationstack 106 having slots 108, can be a larger size magnet wire. Thisresults in the motor having the magnet wires 110 wound with the largersize magnet wire having increased power compared with the motor havingthe magnet wires 16 wound with the smaller size magnet wire, yet havingthe same size lamination stack. Thus, a higher output motor having agiven physical size is achieved.

In an alternative aspect of the foregoing, the magnet wires 110 arewound in slots 108 and then compacted, such as by the application ofiso-static pressure, before armature 102 is encapsulated. For example,armature 102, after magnet wires 110 have been wound in slots 108 butbefore armature 102 is encapsulated, is placed in a properly shapedcavity of a fluid bladder, shown schematically as fluid bladder 144 inFIG. 14. The pressure of the fluid in fluid bladder 144 is increased,forcing magnet wires 110 deeper into slots 108. Armature 102 is thenencapsulated, as described above, with the plastic 116 encapsulatingarmature 102 holding magnet wires 110 in slots 108 after plastic 116hardens. In a variation of the above, magnet wires 110 are made ofbondable wire, as described above, which are thermally cured during thecompaction of magnet wires 110 by fluid bladder 144.

With reference to the prior art armature shown in FIG. 3, another aspectof the invention is described. In this aspect of the invention, priorart armature 40 is modified by making it using thermally conductiveplastic as the plastic in which armature shaft 44 and lamination stack42 are insert molded. The thermally conductive plastic forms end spiders48 and slot liners 50 in the manner described above and is also moldedbetween shaft 44 and lamination stack 42 of armature 40 to electricallyinsulate shaft 44 from lamination stack 42. In this regard, thethermally conductive plastic is selected to have adequate thermalconductivity and dielectric strength or electrically insulativeproperties. The thermally conductive plastic can illustratively beKonduit®

In armatures encapsulated in plastic it is important that plastic flashbe prevented from entering the slots in the commutator ring when theplastic is molded. If flash enters the slots in the commutator ring, itmay project outwardly from the slots and create a bump or ridge that thebrushes will contact when the armature rotates.

An aspect of the invention described with reference to FIGS. 17-18prevents flash from getting into the slots of a tang type commutatorring. An armature 300 has a shaft 302 and a lamination stack 304. Acommutator 306 is mounted on one end of shaft 302. Commutator 306includes a copper commutator ring 308, divided into a plurality ofsegments 310, around a cylindrical core 312, with slots 314 betweenadjacent segments 310. Cylindrical core 312 is made of an electricallyinsulative material, such as phenolic.

Each commutator segment 310 has a tang 318 extending from an axial innerend 326. Tangs 318 are electrically connected to ends of the magnetwires (such as magnet wires 110 of FIG. 5) in known fashion.

To form commutator 306, notches 322 are cut around axial inner end ofcommutator ring 308. Notches 322 are positioned so that they are belowthe track followed by the brushes (not shown) of the motor in whicharmature 300 is used and to be at the axial inner ends of slots 314 whenthey are cut. Plastic 316 is next molded in commutator ring 308, such asby insert molding commutator ring 308, to form cylindrical core 312therein. Plastic 316 is illustratively phenolic. Plastic 316 fillsnotches 322.

Slots 314 are then cut in commutator ring 308. Slots 314 extend radiallythrough commutator ring 308 and run axially from an axial outer end 324of commutator ring 308 part way into the plastic 316 that filled notches322.

Commutator 306, shaft 302 and lamination stack 304 are next assembledtogether and the ends of the magnet wires of armature 300 are connectedto tangs 318 in conventional fashion. Shaft 302, with commutator 306,and lamination stack 304 are then placed in a mold 400 (shownrepresentatively in FIG. 19) and plastic 328 (FIG. 17) molded aroundthem to form armature 300 in similar manner to that described above withrespect to FIG. 5 with the following differences. Mold 400 is providedwith projections 402 that fit between tangs 318 over notches 322.Projections 402 prevent plastic 328 from flowing into slots 314 from thesides of slots 314 by providing thin wall flow regions that allow theplastic to freeze off quicker. The plastic 316 that filled notches 322when cylindrical core 312 was molded prevents plastic 328 from flowingaxially into slots 314 from the inner ends 320 of slots 314.

Turning to FIGS. 20 and 21, another aspect of the invention forpreventing flash from getting into the commutator slots in a stuffertype commutator is described. In a stuffer type commutator, inner endsof the segments of the commutator ring have slots into which ends of themagnet wires are pressed.

An armature 501 has a shaft 503 on which commutator 500, which is astuffer type commutator, is mounted in known fashion. As is known, astuffer type commutator, such as commutator 500, has a commutator ring516 with slots 504 between segments 514. Inserts 502 extend part wayinto slots 504 from an inner end 506 of commutator ring 516. Inserts 502are illustratively made of mica or plastic. Ends of magnet wires 510 arepressed into slots (not shown) in ends 508 of segments 514 of commutatorring 516.

Armature 501 is encapsulated by molding plastic 512 around its shaft 503and lamination stack 505 in a manner similar to that described above.The tool or mold used in molding plastic 512 is configured so that itseals around inner end 506 of commutator ring 516 where inserts 502 arelocated in slots 504 of commutator ring 516, such at 518.Illustratively, ends 520 of inserts 502 extend distally beyond the point518 where the tool seals around inner end 506 of commutator 500 and arethus disposed underneath the tool. When plastic 512 is molded, plastic512 is molded around inner end 506 of commutator ring 516 only whereinserts 502 are in slots 504 and plastic 512 is thereby prevented fromflowing into slots 504.

Turning to FIG. 22, another aspect of the invention is described. Anarmature 600 is encapsulated by molding thermally conductive plastic 602around its shaft 604 and lamination stack 606. The tool or mold used tomold the plastic 602 is configured so that the slots 608 between teeth610 of lamination stack 606 are cored out. As used herein, cored outmeans that the plastic 602 is not molded to top surfaces 611 of thelamination teeth 610, so that the plastic molded in the slots 608 isrecessed from the top surfaces of the lamination teeth 610, formingrecesses 612, through which cooling air can flow. By coring out slots608, heat transfer is improved, less plastic is used and recesses 612can be used by tools in subsequent armature manufacturing operations,such as for orienting, locating and/or indexing armature 600. In thisregard, the tool used in molding plastic 602 can have features, such asblades, that fit within slots 608 to form recesses 612 and these bladescan also hold armature 600 in the correct radial position duringmolding. The surface of plastic 602 can be textured to increase thesurface area of the plastic and/or cause turbulence, thus increasingheat transfer, without taking up additional space. The texturing cantake the form of a pattern 613, such as a diamonds, squares, circles,bumps, dimples, and the like. Illustratively, the texturing is done onthe surface of plastic 602 at an end of lamination stack 606 opposite anend of lamination stack 606 where fan 122 is formed.

FIG. 23 shows a variation of the just discussed aspect of the invention.The same reference numbers are used to identify like elements. In FIG.23, when plastic 602 is molded to encapsulate armature 600, integralfeatures are formed, such as fins 614, that increase surface area andcreate turbulence. FIGS. 34 and 35 show differently shaped fins 614,only two of which are identified by reference numeral 614 therein.

FIG. 24 shows another variation of the just discussed aspect of theinvention. The same reference numbers are used to identify likeelements. In FIG. 24, plastic 602 is molded so that a necked down region616 is formed between the lamination stack 606 of armature 600 andcommutator 618, which reduces the amount of plastic required. Thesurface of plastic 602 is textured as described above to enhance heattransfer, or features such as fins 614 (FIG. 24) formed thereon.

In addition to or in lieu of forming the features such as recesses 612,texture pattern 613, fins 614 and necked down region 616 during moldingplastic 602, they can be formed in secondary operations such as milling,turning or grinding. However, forming these features during moldingplastic 602 allows less plastic to be used than if the plastic 602 isremoved from armature 600 during a secondary operation to form thefeature.

Turning to FIGS. 25-27, another aspect of the invention is describedthat provides better thermal conductively than that provided by usingthermally conductive plastics, which typically have a thermalconductivity in the 1 to 10 W/m-K. Features 700 are insert molded ontoarmature 102 during the molding of plastic 116 or features 700 aremolded from plastic 116 and then metallized. Features 700 mayillustratively be a finned metal or ceramic end coil cover 700′ that isinsert molded onto armature 102 during the molding of plastic 116.Plastic 116, which is illustratively thermally conductive plastic asdescribed above, is molded to form a thin layer between end coils 117 ofmagnet wires 110 and the finned end coil cover 700.′ With specificreference to FIG. 25, finned end coil cover 700′ also includes a fan 702shown in phantom in FIG. 25 affixed thereto or formed integrallytherewith. In a variation, finned end coil cover 700′ is molded from athermally conductive plastic having a higher thermal conductivity thanplastic 116. With specific reference to FIGS. 25 and 27, features 700,such as fins, posts, or blades which are designated as 700″ in FIG. 27,are molded out plastic 116 when plastic 116 is molded to encapsulatearmature 102. End domes 704 including the features 700″ are then coveredwith a thin metallic layer 706, such as by metallizing them with a vapordeposition or other metallization process.

In another aspect of the invention, the plastic, such as plastic 116(FIG. 5) molded around lamination stack 106, portions of commutator 114and armature shaft 112 helps hold lamination stack 106 and commutator114 on armature shaft 112 and improves twist torque. Twist torque, asthat term is commonly understood, is the amount of torque differentialbetween armature shaft 112 and lamination stack 106 or commutator 114that can be withstood before armature shaft 112 turns within laminationstack 106 or commutator 114. In a variation of this aspect of theinvention, an armature shaft 112 a (FIG. 28) is provided with featuresthat interlock with the plastic 116 molded around them to furtherimprove twist torque. These features can include one or more flats 710,projections 712, or other features that interlock with the plastic 116when plastic 116 is molded around them.

Turning to FIGS. 29 and 30, another-aspect of the invention is describedwhere the armature is a double insulated armature. Elements in FIGS. 29and 30 common to the elements in FIG. 5 are identified with the samereference numerals.

FIG. 29 shows a double insulated armature 800 having a protectinginsulating sleeve 802 disposed around shaft 112. Commutator 114 andlamination stack 106 are mounted on shaft 112 with insulating sleeve 802disposed between lamination stack 106 and shaft 112 and betweencommutator 114 and shaft 112. Armature 800 includes magnet wires 110wound in slots 108 of lamination stack 106. Plastic 116 is molded overthe armature 800 so that the plastic 116 flows into and through each ofthe slots 108 and around end coils 117 of magnet wires 110.

Armature 800 is illustratively formed by first placing insulating sleeve802 on shaft 112. It should be understood that insulating sleeve can bemade of other materials, such as high-temperature, glass reinforcedthermosetting resin. It could also be preformed and then placed on shaft112. Shaft 112 with insulating sleeve 802 thereon is then in situ moldedwith lamination stack 106, such as by molding plastic 116. Plastic 116is electrically insulative and forms the functional insulation layer onthe axial ends and in the slots 108 of armature 800. In this regard, themold is made so that plastic 116 is molded in slots 108 so as to coatthe walls of lamination stack 106 leaving the remainder of slots 108open, as well as to form the end spiders around the axial ends oflamination stack 106, such as described above with reference to FIG. 3.Magnet wires 110 are then wound in slots 108 and ends of magnet wires110 (FIG. 5) affixed to commutator 114, which has been placed on shaft112 over insulating sleeve 802. The resulting assembly is then placed ina suitable molding tool and plastic 116 molded around the desiredelements of armature 800. Plastic 116 is illustratively a thermallyconductive plastic as described above and it is injection molded aroundthe elements of armature 800. Plastic 116 is also illustrativelyelectrically insulative.

In double insulated armatures, it is important that the protectiveinsulation barrier be complete and uninterrupted. If the insulatedsleeve is bridged by the functional insulation, particularly if thefunctional insulation is a thermally conductive resin, there is thepossibility of excessive leakage currents during overly abusive loads asthe thermally conductive resin's electrical properties, e.g., dielectricstrength and bulk resistivity, deteriorates at nearly destructivetemperatures.

An uninterrupted barrier is easy to achieve when the lamination stack,windings and commutator are all separated from the shaft by theinsulative sleeve, such as when the insulative sleeve runs the entirelength of the shaft such as shown with respect to sleeve 802 and shaft112 in FIG. 29. However, design constraints sometimes do not allow asufficient radial distance for the commutator to be placed on theinsulative sleeve and must be placed directly on the shaft without theinsulative sleeve therebetween. In these cases, the commutator must beconstructed so that its insulation barrier provides reinforcedinsulation spacings and properties.

Turning to FIG. 30, a double insulated armature 810 with commutator 114placed directly on shaft 112 without an insulative sleeve between it andshaft 112 is shown. Insulative sleeve 812 is disposed on shaft 112between lamination stack 106 and shaft 112 and extends axially up tocommutator 114. Any gap between the end of insulative sleeve 812 andcommutator 114 is sealed by high temperature seal 814 and preventsplastic 116, which is illustratively thermally conductive plastic asdiscussed, from flowing into any gap between the end of insulativesleeve 812 and commutator 114 when plastic 116 is molded to encapsulatearmature 810. Instead of seal 814, labyrinths, dams or high temperaturegaskets can be used.

Turning to FIG. 31, an alternative embodiment of a double insulated,encapsulated armature is shown. Armature 900 has lamination stack 106and commutator 114 directly mounted on an internal shaft 902 and isencapsulated with plastic 116, which is illustratively thermallyconductive plastic as discussed. Internal shaft 902 is coupled to anexternal pinion 904 and bearing journal 906 that has a cylindricalcavity 908 lined with a layer of electrical insulation 910. While FIG.31 shows internal shaft 902 received in insulated cylindrical cavity908, it should be understood that bearing journal 906 could be reversedand external pinion 904 received in insulated cylindrical cavity 908.The foregoing embodiment shown in FIG. 31 provides a double-insulatedarmature where the protecting insulation is distinct and discrete fromthe heat generating portions of the armature.

Turning to FIGS. 32-35, a three-plate mold 1000 used for molding plastic116 to encapsulate armature 102 is shown. Elements in FIGS. 32-35 thatare common with elements in FIG. 5 will be identified with the samereference numerals. Three plate mold 1000 is shown in a molding machine1002, which is illustratively a plastic injection molding machine, witharmature 102 therein. Three plate mold 1000 includes core plate 1004,cavity plate 1006 and runner plate 1008. Core plate 1004 has a generallycan shaped cavity 1005 in which armature 102 is received, commutator 114first. That is, armature 102 is received in core plate 1004 withcommutator 114 adjacent an end or bottom (as oriented in FIG. 32) 1010of core plate 1004. Core plate 1004 may include a pressure transducerport 1012 in communication with a pressure transducer 1014 therein.

Runner plate 1008 has a hole 1024 therein through which armature shaft112 extends when armature 102 is in mold 1000. In runner plate 1008, arunner 1017 splits into two semicircular runners 1018 (shown in dashedlines in FIG. 33) around hole 1024 in which shaft 112 of armature 102 isreceived when armature 102 is in mold 1000. Semicircular runners 1018form a ring runner 1019. The runner 1017 extends to an exit 1021 of ahot sprue 1022. Cavity plate 1006 includes drop passages 1016 extendingfrom ring runner 1019 in runner plate 1008 to gates 1020. Gates 1020 arepreferably located so that they are between slots 108 of armature 102when armature 102 is in mold 1000 and in spaced relation to ends 107 ofslots 108. With specific reference to FIG. 34, a gate 1020 is locatedbetween and above adjacent slots 108 of lamination stack 106.Consequently, each gate 1020 feeds two slots 108 of lamination stack106.

With specific reference to FIG. 36, core plate 1004 may have keys 1026that engage slots 108 in lamination stack 106 of armature 102 to locatearmature 102 in mold 1000 so that gates 1020 are disposed betweenadjacent slots 108 of lamination stack 106. Illustratively, each slot108 has one of keys 1026 projecting into it, which key illustrativelyextends the length of that slot 108. The keys 1026 are preferably sizedto provide thin wall flow regions before the outside diameter oflamination stack 106. This causes plastic 116 to start freezing offbefore it reaches the outside diameter of lamination stack 106,minimizing the chance of flashing to the outside diameter of laminationstack 106. Also, locating gates 1020 between slots 108 may preventplastic 116 from “jetting” down the slots 108 before filling thin wallareas above the coils of magnet wires 110. This is important with mostthermally conductive plastics in that once the melt front stops, thethermally conductive plastic quickly freezes and won't flow again. Thus,if the plastic 116 “jets” down the slots, it may not be possible to packout the thin wall areas afterwards.

In operation, armature 102 (in its pre-encapsulated state) is placed incore plate 1004 of mold 1000, commutator 114 first. Cavity plate 1006 isthen closed over the other end of armature 102 and runner plate 1008closed over cavity plate 1006. Plastic 116 is then injected into mold1000, flowing from hot sprue 1022 through runner 1017 into semicircularrunners 1018 of ring runner 1019, through drop passages 1016 in cavityplate 1006, through gates 1020 and around armature 102 in mold 1000. Itshould be understood that other gate configurations can be used, such asring and flash gates on three-plate molds and tab gates on two-platemolds.

The pressure in the cavity of mold 1000 is monitored using pressuretransducer 1014. Port 1012 in core plate 1004 is illustrativelypositioned toward bottom 1010 of core plate 1004 so that the pressure inthe cavity of mold 1000 is monitored generally at the opposite ends ofwhere gates 1020 are located. When the pressure in the cavity of mold1000 reaches a predetermined level, as sensed by pressure transducer1014, the injection molding machine is switched from its fill stage toits packing stage. As is known, during the fill stage, the shot pressureis high. Once the mold cavity is nearly filled, the injection moldingmachine is switched to the packing stage where the shot pressure isbacked off to a lower level. The shot pressure is then maintained atthis lower level until the plastic hardens, typically determined bywaiting a set period of time. By using the pressure in the cavity ofmold 1000 to determine when to switch from the fill stage to thepackaging stage, as opposed to constant molding parameter such as shotsize, injection time, etc., effects of variations in the materialproperties of the plastic can be reduced.

Illustratively, this predetermined pressure is set at a level thatindicates that the cavity of mold 1000 is nearly filled with plastic116. A technique known as “scientific molding” is illustratively used tocontrol injection molding machine 1002 to minimize the chance offlashing at commutator 114. One such scientific molding technique is theDECOUPLED MOLDING^(SM) technique available from RJG Associates, Inc. ofTraverse City, Mich.

Pressure transducer 1014 could also be used to determine if a part ismolded correctly. That is, a determination is made whether the pressurein the cavity of mold 1000 reached a sufficient level so that the cavityof mold 1000 was completely filled. If not, the part is rejected. Inthis regard a good/bad indicator may be driven based on the monitoredpressure in the cavity of mold 1000 to alert the operator of injectionmolding machine 1002 whether the molded part is good or bad. Injectionmolding machine 1002 may also be configured to automatically accept orreject a part based on the monitored pressure.

Referring to FIG. 37, a mold 1100, which is illustratively a two-platemold, is shown schematically. Two plate mold 1100 is formed to haveoverflow tab cavities 1102 to allow overflow tabs 1104 to be formed whenplastic 116 is molded to encapsulate armature 102. Illustratively,overflow tabs are formed adjacent commutator 114. Overflows tabs 1104help control molding pressure at commutator 114, helping to preventflash while still providing a complete fill and encapsulating of magnetwires 110 with plastic 116. Gates 1106 extend from cavity 1108 of mold1100 to each overflow tab cavity 1102. Gates 1106 are sized so that asmolding pressure builds up in cavity 1108, the plastic 116 flows intothe overflow tab cavities 1102 before flashing over commutator 114.Because most thermally conductive plastics set up quickly, delaying themelt front at the commutator 114 enables the plastic 116 to freeze offin the area of commutator 114 so that when the overflow tab cavities1102 are full and the pressure in cavity 1108 continues to build up, therisk of flash over commutator 114 is minimized or eliminated. Thede-gating process would illustratively accommodate the overflow tabs1104 as additional runners that are removed during the de-gating processso that no additional cycle time results. It should be understood thatoverflow tabs 1104 can be any shape or size sufficient to delay thebuild-up of pressure in mold 1100.

In another aspect of the invention, features that may illustratively bemolded when the armature, such as armature 102, is encapsulated withplastic, such as plastic 116, but that must be physically robust, can bepre-formed, such as by pre-molding them out of a sufficiently strongplastic, and then insert molded when the armature is encapsulated. Thisallows the use of a thermally conductive plastic that does not providethe physical robustness required by these features but has otherproperties, such as better thermal conductivity, than the plastics thatprovide the physical robustness required by these features. Withreference to FIG. 5, fan 122 is an example of a feature that requires acertain degree of physical robustness. Fan 122 can be pre-formed, suchas by pre-molding it if a plastic that provides the necessary physicalrobustness and then insert molded to attach it to armature 102 whenarmature 102 is encapsulated with plastic 116. Plastic 116 can then beselected from plastics having the optimum characteristics forencapsulating armature 102 even if such plastics do not provide thephysical robustness needed by fan 122. This would permit a lower costmaterial to be used for plastic 116 than would be the case if plastic116 is also used to mold fan 122 in the manner discussed above. Use ofthe higher cost plastic that provides more robust physicalcharacteristics would then be limited to those features that require thegreater degree of physical robustness. This would also permit a plastichaving high thermal conductivity but that is structurally weak or haslittle impact strength to be used for plastic 116 with fan 122 beingpre-formed of the higher strength plastic.

While foregoing aspects of the invention have been described withreference to an armature of an electric motor, many of the principlesare applicable to other coil structures used in dynamoelectric machines,such as stators for electric motors and coil structures for generatorsand alternators. FIG. 15 shows a stator 150 for an electric motor, suchas motor 100 (FIG. 5). Stator 150 includes a lamination stack 151 havinga plurality of slots 152 therein. Magnet wires 154 are wound in slots152 to form coils 156. Thermally conductive plastic 158 is molded atleast partially around magnet wires 154 and preferably completelyencapsulates magnet wires 154. Similarly, the surface of plastic 158 canbe molded with features, such as fins, or textured to enhance heattransfer, the features metallized, or features pre-formed and insertmolded when plastic is molded around magnet wires 154.

FIG. 16 illustrates the application of the invention described withrespect to FIG. 3 to a stator. A stator 250 has a lamination stack 252.Lamination stack 252 has a plurality of slots 254 lined with slot liners260 made of thermally conductive plastic. Magnet wires 256 are wound inslots 254 forming coils 258. Thermally conductive plastic is molded inslots 254 to form slot liners 260, which electrically insulate magnetwires 256 from lamination stack 252 as well as enhance heat transferfrom magnet wires 256. In this regard, the thermally conductive plasticis selected to have a desired thermal conductivity and dielectricstrength or electrically insulative properties.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A method for forming an electric motor for a power tool, comprising:forming an armature, including: placing an electrically insulativesleeve on an armature shaft; after the eclectically insulative sleevehas been placed on the armature shaft, securing a lamination stackhaving slots therein on the armature shaft and securing a commutator onone end of the armature shaft; winding magnet wires in the slots in thelamination stack and securing ends of the magnet wires to thecommutator; and after winding the magnet wires in the slots and securingends of the magnet wires to the commutator, molding thermally conductiveplastic to at least partially encase the magnet wires in plastic, thethermally conductive plastic having a base polymer that is a blend of atleast two polymers; disposing the armature in a stator to form theelectric motor.
 2. The method of claim 1, wherein the base polymer is ablend of at least two of nylon, PPS, PPA and LCP.
 3. The method of claim1, wherein the base polymer is a blend of PPS and at least one of nylon,PPA and LCP.
 4. The method of claim 1, wherein the base polymer is ablend of about ninety percent PPS and about ten percent LCP.
 5. Anelectric motor for a power tool, comprising: a stator; an armaturedisposed in the stator, the armature comprising: a lamination stackhaving slots therein; an armature shaft extending coaxially through thelamination stack; a plurality of magnet wires wound in the slots of thelamination stack; a commutator disposed on the armature shaft to whichends of the magnet wires are electrically coupled; and thermallyconductive plastic at least partially encasing the magnet wires, thethermally conductive plastic having a base polymer that is a blend of atleast two polymers.
 6. The motor of claim 5, wherein the base polymer isa blend of at least two of nylon, PPS, PPA and LCP.
 7. The motor ofclaim 5, wherein the base polymer is a blend of PPS and at least one ofnylon, PPA and LCP.